Electron beam parametric amplifier with additional dipole means in pump section



Nov. 30, 1965 R. ADLER ELECTRON BEAM PARAMETRIG AMPLIFIER WITH ADDITIONAL DIPOLE MEANS IN PUMP SECTION Filed Dec. 6, 1963 United States Patent 3 221 264 ELECTRON BEAM FARAMETRIC AMPLIFIER WITH ADDITIONAL DIPOLE MEANS IN PUMP SECTION Robert Adler, Northfield, Ill., assignor to Zenith Radio Corporation, Chicago, 111., a corporation of Delaware Filed Dec. 6, 1963, Ser. No. 328,698 8 Claims. (Cl. 330-43) This invention pertains to electron beam devices and, more particularly, has to do with electron beam parametric amplifiers.

Since the advent of the electron beam parametric amplifier, considerable effort has been expended to extend the operational characteristics of many different forms of this device. Particular attention has been given to the achievement of increased gain. While even the first-disclosed versions provide substantial amplification even at very low noise figures, a demand persists for still higher gain levels.

One limitation upon gain has been noise-orbit pumping. However, since an increase in space charge causes a larger radial drop in beam potential, a reduction of D.C. voltage on the quadrupole to a value close to the point of beam collapse but which affords maximum gain provides inherent protection against noise-orbit pumping in the transverse-mode device. This permits the use of comparatively high pump powers with attendant high gain. Yet, in certain tube versions wherein the DC. potential on the pump section cannot be sufiiciently reduced, even lengthening of the quadrupole does not produce a sufficient improvement in gain. In general, it has been found that a reduction of beam diameter as compared with the pump electrode diameter allows a significant increase in obtainable gain. The gain limit is typically evidenced by interception of electrons by the pump section electrodes.

In noise-orbit pumping, the thermal electron orbits are actually pumped. However, as mentioned above, spacecharge within the beam detunes the noise-orbits and tends to prevent their being pumped to a significant extent in the aforementioned devices. Consequently, this particular phenomenon does not seem to limit the total gain although it does limit the gain per unit length along the beam path in the pump section.

Input transients are another gain-limiting factor. Sudden entry of the electrons into a pumping field can produce a ringing at the electron resonant frequency, which ringing signal is capable of being pumped. In actual practice, fringing at the beginning of the pump section attenuates this effect, and it can be further reduced or avoided completely by constructing the pump section so that the pumping field intensity increases gradually in the downstream direction. This can be accomplished by flaring the quadrupole electrodes or by shorting those electrodes at the upstream end of the pump section,

Still another gain-limiting parameter is the focusing of the beam. Incorrect focusing produces radial electron velocities which may lead to scalloping of the beam envelope. Such scalloping of the beam motion is amplified in the pumping field. Due to space-charge effects, protection against excessive deleterious effect is inherent in the same way as in the case of noise-orbit pumping.

3,221,264 Patented Nov. 30, 1965 But there is one beam operating condition which appears to be capable of substantially affecting the maximum gain that can be obtained. In the cyclotron-wave electron beam parametric amplifier, the electrons are subjected throughout the tube to a longitudinal magnetic field having lines of flux parallel to the beam path. When the beam, because of slight misalignment of the parts relative to the beam path or to the flux lines of the magnetic field, initially is launched at an angle with respect to the flux lines, the beam takes the shape of a stationary corkscrew. This corkscrew wave is substantially amplified by the pumping field. While protection against the corkscrew effect can be obtained by most careful centering, the precision of such centering becomes increasingly critical as the gain is raised.

It is a general object of the present invention to provide an electron beam parametric amplifier in which the adverse effects of the aforementioned corkscrew wave are obviated.

It is another object of the present invention to provide an electron beam parametric amplifier in which the beam centering tolerances are increased.

In accordance with the present invention, an electron beam device comprises means for projecting an electron beam along a predetermined path together with means for subjecting the beam to a magnetic field which establishes a condition of transverse electron resonance for the electrons. Any inclination of the beam relative to the flux lines of the magnetic field results in the development on the beam of a zero-frequency cyclotron or corkscrew wave. Disposed along the beam path is an electron coupler responsive to input signal energy to develop on the beam a transverse electron wave representing the input signal energy. A pump section, including a plurality of electrodes disposed about the beam path and coupled across a pump source of predetermined frequency, subjects the electrons to a periodic inhomogeneous field of a periodicity so related to the motion. of the electrons as to increase the magnitude of the input signal electron wave. Also included in the pump section is means for developing a dipole field across the path to interact with the beam at the predetermined frequency. Finally, there is an output coupler across the path to extract signal energy from the beam.

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to the following description taken on conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is a diagrammatic perspective view of one embodiment of the present invention; and

FIGURE 2 is a fragmentary diagrammatic perspective view of an alternative embodiment of the present invention.

As shown in FIGURE 1 for the purpose of illustrating the present invention, an electron beam device includes an envelope 10 within which an electron gun 11 projects a stream or beam of electrons along a predetermined path, generally coinciding with the longitudinal axis of envelope 10, to a collector 12. Electron gun 10 may be entirely conventional and, as illustratedincludes a cathode 13, a focus electrode 14, and an anode 15 for developing a smooth beam which, in the presence of a longitudinal magnetic field to which the electrons are subjected throughout the beam path, has a constant diameter. The magnetic field is conveniently developed by disposing envelope within a solenoid; in FIGURE 1 it is indicated by the arrow H.

Disposed in succession along the beam path are an input coupler 17 coupled to an input signal source 18, a pump section 19 coupled across a pump source 20, and an output coupler 21 across which a load 22 is coupled. In this instance, input coupler 17 and output coupler 21 are Cuccia couplers each composed of a pair of deflection plates 24, 25 spaced on opposite sides of the beam. Pump section 19 includes, for purposes of the instant discussion, four electrodes spaced circumferentially around the beam path and arranged in opposing pairs 26 and 27. The two pairs are coupled across pump source 20.

In operation, deflectors 24 and 25 in the input section constitute an electron coupler which responds to the input signal energy to develop on the beam a transverse electron wave representing the input signal energy. Pump section 19 subjects the electrons to a periodic inhomogeneous field the periodicity of which is so related to the motion of the electrons as to increase the magnitude of the input-signal electron wave. The parametric amplification relationship is satisfied by assigning values so that the input signal frequency plus the idler frequency inherently developed by the parametric pumping process equals the pump frequency. The design of the individual elements must satisfy the relationship that the sum of the propagation constants of the input signal and idler waves equals the propagation constant of the pumping wave. After amplification, the signal energy is extracted by output coupler 21 and fed to load 22.

A fuller theoretical explanation of the electron beam parametric amplifier, together with a disclosure of many variations thereof, is to be found in British Patent 929,015 published June 19, 1963. Further, a complete explanation of the parametric process as well as the operation of the device in FIGURE 1, as thus far described, may be found in the October 1959 issue of the Proceedings of the IRE at pages 1713 to 1723, in an article entitled The Quadrupole Amplifier, a Low-Noise Parametric Device by R. Adler et al.

The present invention concerns itself with the elimination of adverse gain-limiting effects from a beam wave additional to the input-signal wave. Any misalignment of the electron beam relative to the flux lines of magnetic field H causes the beam to assume a corkscrew shape. An analysis of the corkscrew reveals that it is a cyclotron wave of zero frequency. Since the quadrupole pump section does not distinguish between input signal frequencies, it amplifies the corkscrew wave. The overall gain of the device may therefore be limited by interception of electrons by electrodes in the device, and particularly by the quadrupole electrodes.

In the process of parametrically pumping the initial corkscrew wave,- an idler corkscrew wave inherently is produced. Consistent with the basic parametric relationship that the sum of the signal and idler frequencies equals the pump frequency, the idler corkscrew wave has the same frequency as that of the pump since the initial corkscrew wave is of zero frequency. The invention contemplates including means in the pump section for developing a dipole field across the beam path to interact with the beam at the pump frequency. As a passive interaction device, and since the idler corkscrew wave is a fast wave, the dipole coupler sets up on the beam an idler wave of opposite polarity. This is analogous to the operation of output coupler 21 on the amplified signal wave wherein by reason of the interaction process the radial energy of the electrons is attenuated by the interacting field of the coupler plates. Without a growing idler wave on the electron beam, the initial corkscrew wave cannot grow.

As shown in FIGURE 1, the dipole field is created by a pair of electrode elements 30, 31 disposed about the beam path individually between electrode pairs 26, 27 of the quadrupole pump electrodes. In the device illustrated, utilizing Cuccia couplers, the input signal frequency w equals the cyclotron frequency w established by magnetic field H. The pump frequency u is twice the cyclotron frequency. To interact at the pump frequency with a cyclotron wave in this illustrated device, the dipole coupler must have a finite phase velocity. That is, its propagation constant must be the same as that of the idler corkscrew wave with which it is to interact. The necessary propagation constant for the dipole coupler in pump section 19 is generally determined by the following relationship:

where 13 is the propagation constant of the idler corkscrew wave, w is the pump frequency, w is the cyclotron frequency, and a is the electron beam velocity. Since the phase velocities are the reciprocal of the propagation constant, the equation reveals that the dipole coupler will have a finite phase velocity for all cases except in the single instance where the design of the pump section is such that the pump frequency equals the cyclotron frequency in which case the pump section necessarily is assigned a finite phase velocity and the dipole coupler phase velocity is infinite.

In a practical construction, electrode elements 30 and 31 take the form of helical transmission or delay lines, preferably having a flattened shape with the fiat side facing the beam. To strip off the corkscrew idler wave with which the dipole coupler interacts, electrode elements 30 and 31 are coupled across a dissipative load 33 which is matched to the dipole electrode elements, as by the well known Kompfner-dip technique. Alternatively, elements 30 and 31 may be self-loaded, as by being wound with resistive wire, so as also to serve the function of load 33. In order to avoid direct coupling of the pump signal into the dipole coupler from the quadrupole field, the position of elements 30 and 31 should be carefully balanced relative to that field and, hence, relative to the physical posi tion of the pump electrodes.

In the alternative form of the invention depicted in FIGURE 2, the portion of the device within envelope 10' to either side of the illustrated pump section, including the input and output couplers, is the same as in FIGURE 1 and therefore has not been shown. In this instance, the pump section is split into two portions 35 and 36 each of which is a quadrupole electrode assembly identical to that shown in FIGURE 1 except that, for a given amount of input signal amplification, each section may be approximately only half the length of the quadrupole in FIG- URE 1. Further, the two quadrupoles are coupled across a pump source and develop a pumping field in the same manner described above with respect to FIGURE 1. In this instance, the dipole coupler which interacts with the idler corkscrew wave is disposed intermediate pump portions 35 and 36.

As illustrated in FIGURE 2, dipole coupler 37 is in the form of a bifilar helix across the two windings of which an inductor 38 is coupled to resonate the coupler capacity at the pump signal frequency, the frequency of corkscrew wave idler interaction. In parallel with inductor 38 is a resistor 39 which serves as a load to dissipate the energy stripped from the corkscrew idler wave. Inductor 38 and resistor 39 may be either external or internal of envelope 10. Of course, if internal they must be formed of metallic or other elements capable of being degrassed during tube processing. The pitch of bifilar coupler 37 must be selected properly for interaction at the frequency of the idler wave with which it 18 to interact. To this end, the coupler is wound so that:

where N is the number of'helix turns per unit length, N is the number of cyclotron orbits per unit length, F is the cyclotron frequency, and F is the. interaction frequency. For the case illustrated, the pump frequency F is equal to 2F as indicated by the straight quadrupole positions 35 and 36. Because the corkscrew idler wave has the same frequency as the pump, it follows that F=2F and N=N The negative sign indicates that the handedness of the bifilar windings must be opposite to that of a corkscrew traced out by electrons spiralling and moving forward in the given magnetic field.

In the alternative, any other known coupler, of which there are several, for interacting with cyclotron waves at a frequency different from the cyclotron frequency may be employed. Where finite phase velocity transmission lines are employed, as in FIGURE 1, undesired reflections may be avoided by conventional termination techniques.

An electron beam parametric amplifier constructed in accordance with the present invention is characterized by reduced criticality of beam centering. This, in turn, reduces constructional tolerances and enhances operational flexibility.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made therein without departing from the invention in its broader aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications as fall Within the true spirit and scope of the invention.

I claim:

1. An electron beam device comprising:

means for projecting an electron beam along a predetermined path with a velocity a means for subjecting said beam to a magnetic field establishing a condition of transverse cyclotron resonance for the electrons in said beam at a frequency w any inclination of said beam relative to the flux lines of said field resulting in the development on said beam of a zero-frequency cyclotron wave;

an electron coupler along said path and responsive to input signals for developing on said beam a transverse electron wave representing said signals;

a pump section, including a plurality of electrodes disposed about said path and coupled across a pump source of predetermined frequency w for subjecting said electrons to a periodic inhomogeneous field the periodicity of which is so related to the motion of said electrons as to have a phase relationship with said motion to enable the delivery of energy to a component'thereof in proportion to the amplitude of said component and thereby increase the magnitude of said electron wave;

means additionally in said pump section, including a dipole coupler having a propagation constant ,8 assigned in accordance with the relationship:

for developing a dipole field across said path to interact with said beam at said predetermined frequency;

and an output coupler along said path for extracting signal energy from said beam.

2. An electron beam device comprising:

means for projecting an electron beam along a predetermined path with a velocity u means for subjecting said beam to a magnetic field establishing a condition of transverse cyclotron resonance for the electrons in said beam at a frequency ar any inclination of said beam relative to the flux 6 lines of said field resulting in the development on said beam of a zero-frequency cyclotron wave; an electron coupler along said path and responsive to input signals for developing on said beam a transverse electron wave representing said signals;

a pump section along said path, including four electrodes circumferentially spaced around said path with the two pairs of opposing electrodes being coupled across a pump source of predetermined frequency w for subjecting said electrons to a periodic inhomogeneous quadrupole field the periodicity of which is so related to the motion of said electrons as to have a phase relationship with said motion to enable the delivery of energy to a component thereof in proportion to the amplitude of said component and thereby increase the magnitude of said electron wave;

means additionally in said pump section, including a pair-of electrode elements disposed about said path individually between said electrode pairs and having a propogation constant p assigned in accordance with the relationship:

for developing a dipole field across said path to interact with said beam at said predetermined frequency;

and an output coupler along said path for extracting signal energy from said beam.

3. An electron beam device comprising:

means for projecting an electron beam along a predetermined path with a velocity n means for subjecting said beam to a magnetic field establishing a condition of transverse cyclotron resonance for the electrons in said beam at a frequency w any inclination of said beam relative to the flux lines of said field resulting in the development on said beam of a zero-frequency cyclotron wave;

an electron coupler along said path and responsive to input signals for developing on said beam a transverse electron wave representing said signals;

a pump including first and second portions spaced along said path and each having 'a plurality of electrodes coupled. across a pump source of predetermined frequency u for subjecting said electrons to a periodic inhomogeneous field the periodicity of which is so related to the motion of said electrons as to have a phase relationshipwith said motion to enable the delivery of energy to a component thereof in proportion to the amplitude of said component and thereby increase the magnitude of said electron wave;

means, including a pair of electrodes disposed about said path intermediate said portions and having a propagation constant {3 assigned in accordance with the relationship:

B no

for developing a dipole field across said path to interact with said beam at said predetermined frequency;

and an output coupler along said path for extracting signal energy from said beam.

4. An electron beam device comprising:

means for projecting an electron beam along a predetermined path with a velocity u means for subjectingsaid beam to a magnetic field establishing a condition of transverse cyclotron resonance for the electrons in said beam at a frequency w any inclination of said beam relative to the flux lines of said field resulting in the development on said beam of a zero-frequency cyclotron wave;

a first electron coupler along said path and responsive to input signals for developing on said beam a transverse electron wave representing said signals;

a pump section, including a plurality of electrodes disfor developing a dipole field across said path to interact With said beam at said predetermined frequency and including means for resonating said predetermined second coupler at said frequency;

and an output coupler along said path for extracting signal energy from said beam.

5. An electron beam device comprising:

means for projecting an electron beam along a predetermined path with a velocity a means for subjecting said beam to a magnetic field establishing a condition of transverse cyclotron resonance for the electrons in said beam at a frequency w any inclination of said beam relative to the flux lines of said field resulting in the development on said beam of a zero-frequency cyclotron wave;

a first electron coupler along said path and responsive to input signals for developing on said beam a transverse electron wave representing said signals;

'a pump section, including a plurality of electrodes disposed about said path and coupled across a pump source of predetermined frequency u for subjecting said electrodes to a periodic inhomogeneous field the periodicity of which is so related to the motion of said electrons as to have a phase relationship with said motion to enable the delivery of energy to a component thereof in proportion to the amplitude of said component and thereby increase the magnitude of said electron wave;

a second electron coupler additionally in said pump section, having a propagation constant ,8 assigned in accordance with the relationship:

and including means for resonating and loading said second coupler at said predetermined frequency, for developing a dipole field across said path to interact With said beam at said predetermined frequency;

and an output coupler along said path for extracting signal energy from said beam.

6. An electron beam device comprising: means for projecting an electron beam along a predetermined path with a velocity n means for subjecting said beam to a magnetic field establishing a condition of transverse cyclotron resonance for the electrons in said beam at a frequency m any inclination of said beam relative to the flux lines of said field resulting in the development on said beam of zero-frequency cyclotron wave;

' an electron coupler along said path and responsive to input signals for developing on said beam a transverse electron wave representing said signals;

' a pump section, including a plurality of electrodes disposed about said path and coupled across a pump source of predetermined frequency w for subjecting said electrons to a periodic inhomogeneous field the periodicity of which is so related to the motion of said electrons as to have a phase relationship with said motion to enable the delivery of energy to a component thereof in proportion to the amplitude of said component and thereby increase the *magnitude of said electron wave;

means additionally included in said pump section, in-

cluding a dipole coupler having a propagation constant 13 assigned in accordance with the relationship:

responsive to electron motion therebetween at said predetermined frequency for developing a dipole field across said path to interact with said beam at said predetermined frequency;

and an output coupler along said path for extracting signal energy from said beam.

7. An electron beam device comprising:

means for projecting an electron beam along a pre determined path with a velocity u means for subjecting said beam to a magnetic field establishing a condition of transverse cyclotron resonance for the electrons in said beam at a frequency w any inclination of said beam relative to the flux lines of said field resulting in the development on said beam of zero-frequency cyclotron wave;

an electron coupler along said path and responsive to input signals for developing on said beam a transverse electron wave representing said signals;

a pump section along said path, including four electrodes circumferentially spaced about said path with the two pairs of opposing electrodes being coupled across a pump source of predetermined frequency u for subjecting said electrodes to a periodic inhomogeneous field the periodicity of which is so related to the motion of said electrons as to have a phase relationship with said motion to enable the delivery of energy to a component thereof in proportion to the amplitude of said component and thereby increase the magnitude of said electron wave;

means in said pump section, including a pair of dissipatively loaded transmission lines disposed about said path individually between said electrode pairs and having a propagation constant ,B assigned in accordance with the relationship:

for developing a dipole field across said path to interact with said beam at said predetermined frequency;

and an output coupler along said path for extracting signal energy from said beam.

8. An electron beam device comprising:

means for projecting an electron beam along a predetermined path;

means for subjecting said beam to a magnetic field establishing a condition of transverse cyclotron resonance for the lectrons in said beam F any inclination of said beam relative to the flux lines of said field resulting in the development of said beam of zero-frequency cyclotron wave;

an electron coupler along said path and responsive to input signals for developing on said beam a transverse electron wave representing said signals;

a pump including first and second portions spaced along said path and each having a plurality of electrodes disposed about said path and coupled across a pump source of predetermined frequency F, for subjecting said electrodes to a periodic inhomogeneous field the periodicity of which is so related to the motion of said electrons as to have a phase relationship with said motion to enable the delivery of energy to a component thereof in proportion to the amplitude of said component and thereby increase the magnitude of said electron wave;

means disposed intermediate said portions and including a bifilar helix coaxial with said path together With means for resonating and loading said helix at References Cited by the Examiner said predetermined frequency, said helix having 8. UNITED STATES PATENTS 't 'f' th If h': pi Ch Sans e m a ms 1p 2,959,740 11/1960 Adle N 5 3,051,911 8/1962 Kompfner 33041.7

0 e 3,109,146 10/1963 Gordon 3304.7

where N is the number of helix turns per unit length 3,124,756 3/1964 Hrbek 330-47 and N is the number of cyclotron orbits per unit FOREIGN PATENTS length, in order to develop a dipole field across said path and interact with said beam at said predeterl0 g z g iz i mined frequency; Tea H and an output coupler along said path for extracting ROY LAKE Primary Examinw signal energy from said beam. 

1. AN ELECTRON BEAM DEVICE COMPRISING: MEANS FOR PROJECTING AN ELECTRON BEAM ALONG A PREDETERMINED PATH WITH A VELOCITY U0; MEANS FOR SUBJECTING SAID BEAM TO A MAGNETIC FIELD ESTABLISHING A CONDITION OF TRANSVERSE CYCLOTRON RESONANCE FOR THE ELECTRONS IN SAID BEAM AT A FREQUENCY WC, ANY INCLINATION OF SAID BEAM RELATIVE TO THE FLUX LINES OF SAID FIELD RESULTING IN THE DEVELOPMENT ON SAID BEAM OF A ZERO-FREQUENCY CYCLOTRON WAVE; AN ELECTRON COUPLER ALONG SAID PATH AND RESPONSIVE TO INPUT SIGNALS FOR DEVELOPING ON SAID BEAM A TRANSVERSE ELECTRON WAVE REPRESENTING SAID SIGNALS; A PUMP SECTION, INCLUDING A PLURALITY OF ELECTRODES DISPOSED ABOUT SAID PATH AND COUPLED ACROSS A PUMP SOURCE OF PREDETERMINED FREQUENCY WP, FOR SUBJECTING SAID ELECTRONS TO A PERIODIC INHOMOGENEOUS FIELD THE PERIODICITY OF WHICH IS SO RELATED TO THE MOTION OF 